The present invention relates to disk drive systems and, more particularly, to microactuator devices that function to provide fine movements of a transducing head so that densely spaced tracks on a disk may be accurately selected and followed to read and write more data on disk.
The present invention particularly pertains to a microactuator device for use in a multiple track disk drive system so that fine positioning of a transducing head over a selected track of the disk may be obtained, and more particularly, to a piezoelectric microactuator device that provides a simplified, low-cost construction when compared with the prior art designs.
Magnetic disk drives are information storage devices that use thin film magnetic media to store data. A typical disk drive as seen in FIG. 7 of U.S. Pat. No. 6,166,890, the disclosure of which is incorporated herein, includes one or more rotatable disks having concentric data tracks in which data is read or written. As a disk rotates, a head transducer, also referred to as a magnetic recording head, is supported by a slider and positioned by an actuator element to magnetically read data from, or write data to, various tracks on the disk. Typically, the head transducer is attached to a slider having an air-bearing surface, which is supported adjacent to a data surface comprising the data tracks by a film of air generated by the rotating disk. Suitable wires connect the transducer on the slider to a data processing unit that controls read/write electronic circuitry.
The radial spacing between data tracks continues to decrease with increase in recording density, requiring greater precision for head positioning. External and internal disturbances in a disk drive continuously move the head transducer off the data track. Conventional disk drives correct for off-track motion by actuating the arms carrying the head transducers using a voice coil motor. See the Figures of U.S. Pat. No. 6,115,223, the disclosure of which is incorporated herein by reference. However, a voice coil motor lacks fast response and sufficient resolution for small motions required to effectively maintain position of head on a track of a high-track density disk. Therefore, a secondary fast response high-resolution head positioning mechanism is necessary for small motions to reduce track registration error in high-density disk drives.
Various prior art piezoelectric microactuator designs correct for hard disk drive disk track misregistration. These include designs with piezoelectric elements mounted on arm, or on suspension near hinge, near or under the slider carrying the head transducer. Designs with piezoelectric microactuators mounted on the arm produce highest slider movement but excite undesirable voice coil motor coil, arm, and suspension load beam modes. Designs with piezoelectric microactuators mounted near the hinge produce medium slider movement but excite undesirable arm tip and suspension modes. Designs with piezoelectric microactuators mounted near the slider produce small slider movement but excite minimum undesirable modes of flexure and load beam.
Some of the currently available designs, the piezoelectric elements are placed under the slider (between slider and flexure) thereby increasing disk-to-disk spacing and reducing volumetric storage capacity. The present invention has elements placed on the side of the slider without increasing the disk to disk spacing and having no adverse impact on recording density.
The Japanese patent No. 62-287480 disclosed a very unique piezoelectric microactuator arrangement. This reference discloses the placement of piezoelectric microactuators at 1 to 4 corners of the slider or perpendicular to a side of the slider. This approach requires a large space near the head and is not suitable for disk drive suspension application since it significantly reduces disk recordable area because of the large in plane space requirement. The Japanese patent No. 6-150596 discloses the installation of the piezoelectric element inside a cavity in the slider. In this approach, the slider effective thickness is reduces, which will result in higher slider distortion problems. To compensate for the reduction in the slider effective thickness, the slider must be made thicker. The thicker slider results in a higher disk-to-disk spacing. U.S. Pat. No. 4,583,135 shows helical scanning VTR tracking device that utilizes thickness extension mode (d33) of the piezoelectric element. This approach requires many pieces of piezoelectric elements to achieve desired stroke. The additional piezoelectric elements would increase the mass of the overall structure. The increased mass of the overall structure degrades the dynamic performance, while requiring additional space. The additional space results in reduction in the data recording area.
Designs with piezoelectric elements on the leading edge of the slider have small stroke, are limited in track misregistration correction and are expensive to manufacture. Designs with piezoelectric microactuators mounted in the same plane and near the slider have more complex mechanisms like a cradle, are more fragile, excite more undesirable dynamic modes and are more expensive to manufacture.
The present invention relates to piezoelectric microactuator locations near the slider and in the same plane as slider, and differs from others with location in between slider and flexure, for not adding to the slider thickness and disk-to-disk spacing that reduces drives volumetric storage capacity. This invention also provides an alternate U-shape piezoelectric microactuator element placed in the same plane and around the slider for increased placement accuracy, better dynamics, and increased head movement that is not seen in the prior art.
In one embodiment, the present invention utilizes two rectangular shaped piezoelectric elements placed on the two sides of the slider with ends of both elements attached to the fixed and movable parts of a T-shaped flexure that in turn is attached to a load beam that is fixed. The piezoelectric elements are polarized in opposite direction, such that when a voltage is applied to their top and bottom surfaces, one of the two piezoelectric elements expands and the other contacts, resulting in off-track rotary motion of the slider and head transducer attached to the slider. The rotary motion results in off-track motion that is used by drive servo system to help position the head accurately and fast, and make real time correction, as the head tends to move off track due to disturbances caused by external and internal vibrations. The two piezoelectric elements can also be connected at flexure end to make a single U-shape element for ease of assembly and accurate positioning. The two sides of the U-shape piezoelectric elements are polarized in either the opposite or same direction. The opposite polarization produces a rotary motion, while the same direction polarization produces translatory motion of the slider. Both motions result in across-track motion of the head transducer when the voltage is applied to the top and bottom surfaces of the U-shape piezoelectric element.
Briefly stated then, a fundamental provision of the present invention is defined as follows:
a disk drive system having an actuator arm to support a slider carrying a transducing head adjacent a selected data track of a rotatable disk having a plurality of concentric data tracks, the slider having an air-bearing surface generally parallel to and confronting the top surface of the rotatable disk, wherein a microactuator device effects fine positioning of the transducing head with respect to the selected data track, the microactuator device comprising the slider carrying a transducer head; a T shape flexure member with a fixed and moving end and attached to load beam; and two oppositely polarized rectangular piezoelectric elements having opposite ends, wherein these ends are attached to fixed and moving ends of the flexure. Application of voltage to the top and bottom of the piezoelectric elements, resulting in rotary movement of the slider carrying the head transducer to enable fast and accurate tracking of the data on a high density disk. Alternately, the two piezoelectric elements can be attached together on the fixed side of the flexure to make a single U-shape element for high positioning accuracy and ease of placement. The piezoelectric elements could be made of multiple layers of piezoelectric material to increase head transducer movement, recording density and reduce settle time during track seek.
The foregoing and still further objects and advantages of the present invention will be more apparent from the following detailed explanation of the preferred embodiments of the invention in connection with the accompanying drawing.